Analysis of slope-stabilising piles with the shear strength reduction technique

In this paper, the ultimate limit state (ULS) of continuous and discontinuous pile rows in a frictional soil slope is investigated by performing 2-D and 3-D numerical analyses, respectively. The ‘phi-ci reduction calculation’ implemented in PLAXIS was adopted to analyse the ULS conditions of a pile row embedded in an infinite slope, including a slipping layer under residual conditions, placed between unstable upper and stable lower soils. For a continuous pile row, pile displacements and soil stress at the pile interface that vary with the embedment ratio are discussed while highlighting the role of the unstable layer on the collapse of the system. Indeed, the results of parametric analyses with respect to changes in the slope inclination and residual frictional angle on the slipping surface are also represented in dimensionless form. The minor influence of these two variables on the problem is proven. For discontinuous pile rows, the soil arching effect was investigated with a focus on the influence of the pile embedded length on the critical spacing value beyond which soil arching vanishes. The different behaviours of a pile in a row between a continuous wall and isolated pile are also analysed in depth. The ultimate loads computed by the 2-D and 3-D analyses are compared to analytical rigid-plastic solutions obtained by extending the existing solution in frictional soils for a single pile and for a continuous wall to discontinuous pile rows. Finally, simple charts to design stabilising pile rows inside a landslide at the ULS are provided.